This invention relates in general to extrusion devices and methods and in particular to a new and useful method of producing composite laminates wherein both a support and a coating are extruded through a sheet die after they are conducted separately to the die through different channels.
The invention relates to a method of producing composite boards or laminates where a support of acrylic nitrile-butadiene-styrene (ABS) and a coating of polymethyl methacrylate (PMMA, acylic glass) are coextruded through a sheet die.
To the extent that such methods have become known until now, the materials to be combined were first extruded, then brought together in an adapter and bonded, and only then extruded jointly through a sheet die. This presents no difficulties as long as the materials to be joined have comparable viscosities at a given temperature. This is the case for the material pair ABS/acrylic glass for example when the melt flow index MFI 230.degree. C./3.8, measured according to DIN 53735, has a value of about 6.
A study of the life of bathtubs which had been produced by deep-drawing of plates made in conventional manner showed that after about 500 hot-cold water cycles the first hair fissures became visible in the acrylic glass surface. This value is sufficient for only modest requirements, and the problem arose to substantially increase the number of alternate hot and cold water fillings to which a tub could be subjected without visible damage.